Lifting clamps

ABSTRACT

A lifting clamp comprises a housing having fixed and movable jaws positioned to grip and hold loads of varying thickness therebetween. The movable jaw or cam, as it is sometimes referred to in the art, is actuated by a link and lever connection to a radius link pivotally mounted on said housing, which said link is also connected to means such as a crane for applying lifting force to the clamp to lift the load, the leverage being such that the greater the lifting force required to lift the load, the greater the gripping force applied to the load by the movable jaw. The radius link can be moved to open or close the jaws by a hand lever pivotally mounted on said housing, and means are provided for applying spring pressure to said radius link to lock said movable jaw in open position, and in various closed positions depending on the thickness of the load.

United States Patent [191 Kopp Nov. 20, 1973 Primary Examiner-Evon C. Blunk Assistant Examiner-Johnny D. Cherry Attorney-Nichol M.' Sandoe et al.

Z4 I A I 22 23 l II v 28 I 3 I 9 [57] ABSTRACT A lifting clamp comprises a housing having fixed and movable jaws positioned to grip and hold loads of varying thickness therebetween. The movable jaw or cam, as it is sometimes referred to in the art, is actuated by a link and lever connection to a radius link pivotally mounted on said housing, which said link is also connected to means such as a crane for applying lifting force to the clamp to lift the load, the leverage being such that the greater the lifting force required to lift the load, the greater the gripping force applied to the load by the movable jaw. The radius link can be moved to open or close the jaws by a hand lever pivotally mounted on said housing, and means are provided for applying spring pressure to said radius link to lock said movable jaw in open position, and in various closed positions depending on the thickness of the load.

10 Claims, 6 Drawing Figures PAIENTEU U 3 3,773,377

sum 2 OF 4 'FIG.3

1 LIFTING CLAMPS This invention relates to lifting clamps having fixed and movable jaws between which a load to be lifted may be securely gripped. The loads lifted by such clamps are sometimes of great weight, frequently several tons, and are sometimes lifted to considerable heights. If the load slips from the clamp there is danger of serious damage to personnel and to equipment and property. It is of paramount importance, therefore, that the load be gripped securely by the clamp at all times, i.e. from the time when it is first gripped until it is intentionally released from the clamp. The possibility of accidental or unintended release must be reduced to a minimum, particularly at times when the load is being deposited on a supporting surface or member, at which time it may be subjected to jolting or other stresses tending to loosen or release the grip.

The loads lifted by such clamps also vary considerably in thickness. For example, such clamps are widely used as plate clamps for lifting heavy steel plates and slabs'which may vary in thickness from about 0.25 inch to 4 inches or inches or even more. A satisfactory clamp must be capable of gripping loads having a wide range of thicknesses.

It is known in the art to provide such lifting clamps in which it is said to be possible to lock themovable jaw in both its open and closed positions, but in most cases the lock consists merely of a spring having one end connected to the movable jaw and the other end connected to the housing through a pivoted overcenter arrangement such that it may be operated by a lever to apply stress directly to the movable jaw tending to hold it in either its open or closed position, as desired. However, a lock of this type can be opened rather easily from the closed position if external force is applied to the movable jaw sufficient to overcome the stress applied directly thereto by the spring.

It is an object of the present invention to provide a lock device for lifting clamps of this type in which the spring pressure applied to the movable jaw in both its open and closed positions is applied indirectly through a link and lever mechanism in which the mechanical advantage is such that it is virtually impossible to move the movable jaw from either of its locked positions by external force applied thereto.

Other objects and advantages of the invention will appear hereinafter.

A preferred embodiment of the invention selected for purposes of illustration is shown in the accompanying drawings, in which,

FIG. 1 is a bottom plan view of the clamp looking toward the jaws in which the movable jaw is in open position.

FIG. 2 is a side elevation.

FIG. 3 is a section on the line 3-3 of FIG. 2 in which the movable jaw is in open position.

FIG. 4 is a section on the line 4-4 of FIG.2 in which the movable jaw is in closed position to clamp a relatively thick load.

FIG. 5 is a side elevation partly in section and partly broken away in which the movable jaw is in closed position to clamp a relatively thin load.

FIG. 6 is a section on the line 6--6 of FIG. 5.

The clamp shown in the drawings is of the type known as a plate clamp designed and adapted for lifting heavy steel plates. It will be understood, however, that the lock device of the invention may be applied to other types of clamps in which a load is gripped between jaws.

Referring to the drawings, and in particular to FIGS. 1, 2 and 3 in which the clamp is shown with its movable jaw in the open position, the clamp comprises a housing having parallel side plates 1, 2 spaced apart by blocks 3, 3 and connected in any suitable manner'as by rivets or bolts (not shown). A slot 4 is formed'in each of the side plates of sufiicient width to receive a load 5 of the maximum thickness for which the clamp is designed. The formation of the slot provides two depending legs 6 and 7 in the housing plates. The legs 6 which carry a serrated gripping pad 8 mounted in the block 3 constitute the fixed jaw of the clamp. The other leg 7 carries the movable jaw 9 which is pivotally mounted on the. pivot pin 10 which extends through the side plates 1, 2. The movable jaw has a serrated gripping surface 1 1 which is curved eccentrically with respect to the axis of pivot pin 10 in accordance with common practice in the art.

The movable jaw 9 is pivotally connected to the ends of links 12 by the pin 13, with the other ends of said links pivotally connected by pin 18 to a lifting shackle 14 adapted to be engaged by the hook 15 of a crane or other lifting equipment.

A radius link 16 is pivotally mounted on the housing by pin 17 and has arms extending in opposite directions from the pivot. One arm is pivotally connected near its end to the links12 and shackle 14 by the pin 18. Pin 17 is mounted to rotate on the plates 1, 2. The radius link pivots freely on the pin 17, but the lever link 19 and hand lever 20, both of which are mounted on the pin 17, are keyed thereto so that rotating movement of the hand lever 20 causes the lever link 19 to rotate in the same direction. Lever link 19 is located within the housing between the plates 1, 2 but the lever 20 is located outside the housing on an extension of the pin 17 which projects beyond the plate 1.

Lever link 19 is pivotally connected by a pin 21 to a pressure foot 22 having a toe 23 and a heel 24. Lever link 19 and pressure foot 22 constitute the two legs of a toggle joint which includes the pin 21 as its knee, the functions of which will be explained hereinafter. A guide rod 25 formed integrally with the pressure foot 22 extends downwardly and into and through an aperture 26 in the pin 27 which is pivotally mounted in the plates 1, 2. The guide rod 25 is slidable freely in the aperture 26 and is surrounded by a compression spring 28 one end of which bears against the pin 27 and the other end of which bears against the pressure foot 22.

The other arm 30 of the radius link terminates in a convexly curved surface positioned to engage the heel 24 of the pressure foot 22 in the open position of the clamp as shown in FIG. 3. The radius link is also provided with a concavely curved surface 32 positioned to engage the curved surface 33 of the toe 23 in the closed position of the clamp as shown in FIGS. 4 and 5.

In the open position of the clamp as shown in FIG. 3 it will be noted that the movable jaw 9 has been swung back into the housing between the plates 1, 2 far enough to clear the slot 4 to receive the load to be lifted. In this position, the pivot pin 21 is offset to the left of the line A connecting the axes of pins 17and 27 so that the compression spring 28, acting on the lever link 19 through pin 21, tends to rotate the lever link in clockwise direction. This causes the heel of the pressure foot to engage the arm 30 of the radius link and apply pressure thereto tending to rotate the radius link in clockwise direction. This, in turn, acting through links 12, applies pressure to the movable jaw tending to lock it firmly in full open position. It is extremely difficult to move the jaw from this position by applying force tending to rotate it toward closed position because such force, transmitted through links 12 to the radius link 16 simply tends to rotate the radius link in counterclockwise direction causing the arm 30 to apply pressure to the heel 24. While this may tend to rotate the lever link 19 in counterclockwise direction, the downward component of the applied force is small and very great force would have to be applied to the movable jaw to overcome the opposing force applied by the compression spring 28.

Referring now to FIG. 4, the clamp is shown with the movable jaw in closed position in gripping engagement with the load. In order to move the clamp to closed position from the open position of FIG. 3, the hand lever 20 is moved in counterclockwise direction causing the lever link 19 to move in counterclockwise direction. As it does so, the axis of pin 21 moves overcenter, i.e. it passes the line A connecting the axes of pins 17 and 27, and as it continues its movement, the surface 33 of the toe 23 moves toward and engages the curved surface 32 of the radius link. During this movement, the heel of the pressure foot 22 has moved away from the arm 30, thus freeing the radius link to swing in counterclockwise direction when the surface 32 is engaged by the surface 33. The spring 28 now exerts pressure on the radius link through the pressure foot 22 causing the radius link to swing in counterclockwise direction. This movement, in turn, acting through links 12, causes the movable jaw to grip the load.

As previously noted, in the closed position of the clamp, the lever link 19 and pressure foot 22, being pivotally connected by the pin 21, constitute a toggle joint which becomes effective in the closed position of the clamp, so that the pressure applied to the radius link by the spring 28 acting through the pressure foot 22 is very great, and becomes greater and greater as the axis of pin 21 moves across and away from the line A connecting the axes of pins 17 and 26 and thus increases the angle between the legs of the toggle joint.

This is of importance for reasons illustrated by a comparison of FIGS. 4 and 5. In FIG. 4, the clamp is shown in closed position with the parts shown gripping a relatively thick load. In FIG. 5, the clamp is also shown in closed position but with the parts shown gripping a load of lesser thickness.

It will be noted that in FIG. the angle between the legs of the toggle joint has increased to an extent such that the axes of the three pivot points are nearly aligned. Bearing in mind that the compression of the spring 28 may decrease somewhat as the axis of pin 21 moves away from the line A connecting the axes of pins 17 and 27, it will be understood that the toggle joint compensates for the decreased compression of the spring. The arrangement is preferably such that the axes of the three pivot points of the toggle joint are brought substantially into alignment by operation of the hand lever when the movable jaw is swung into contact with the gripping pad 8. Thus, the clamp is capable of gripping and lifting loads of a very wide range of thickness.

It will be understood that in the practical operation of such clamps, it is desirable that the serrated surfaces of the gripping pad and the movable jaw actually penetrate and dig into the surface of the load in order to insure that a secure grip is effected. In the parlance of the industry, the clamp is then stuck to the load. In clamps according to this invention the force applied by the spring 28 acting through the toggle joint is usually sufficient to cause an initial penetration of the load by the serrated surfaces as the clamp is closed. Thus, it will be understood that as the pin 21 moves overcenter, the spring pressure causes the pressure foot to snap over and to hit the radius link with considerable force, which when transmitted to the movable jaw causes it to bite into the load. Moreover, since the hand lever moves in the same direction as the lever link 19, pressure applied thereto can assist in causing the movable jaw to bite into the load. This intial penetration will then be increased as lifting force is applied through the shackle 14, thus applying increased gripping force to the movable jaw. As the teeth of jaw 9 penetrate the load 5, the long arm of the radius link 16 which is connected to the lifting shackle 14 moves upward and the convex end 33 of pressure foot 23 moves further along surface 32 of the radius link 16 thus automatically securing lock at the point of furthest jaw penetration.

Meanwhile, before lifting force is applied, after the clamp is closed, the movable jaw is firmly locked in gripping position and it is extremely difi'icult to move the jaw to loosen the grip by forces applied through the load. Such forces transmitted through links 12 to the radius link 16 simply tend to rotate the radius link in clockwise direction to apply pressure to the pressure foot 22. While this may tend to rotate the lever link 19 in clockwise direction, the toggle joint effectively prevents movement because the downward component of the applied force is small and very great pressure would have to be applied to overcome the opposing force applied by the compression spring 28.

When the lifting operation has been completed, and it is desired to release the clamp from the load, the hand lever 20 is swung in clockwise direction to the position of FIG. 5. Again, as the pin 20 moves overcenter, the spring pressure causes the pressure foot to snap over and to hit the radius link with considerable force. This force as transmitted to the movable jaw is usually sufi'icient to release the stuck jaws from the load.

It will be understood that the invention may be variously modified and embodied within the scope of the subjoined claims.

I claim as my invention:

1. A lifting clamp comprising a housing having fixed and movable jaws between which a load may be clamped, a radius link pivotally mounted on said housing, said radius link having arms extending in opposite directions from the pivot, means including a link pivotally connecting one arm of said radius link to said movable jaw to move said jaw between open and closed positions, a spring, and means to transmit pressure from said spring to one arm of said radius link when said link is in jaw opening position and to transmit pressure from said spring to the other arm of said link when said link is in jaw closing position.

2. A lifting clamp as claimed in claim 1 in which said pressure transmitting means includes a pressure foot having a heel positioned to engage a surface of one arm of said radius link when said link is in jaw opening position and having a toe positioned to engage a surface of the other arm of said radius link when said link is in jaw closing position.

3. A lifting clamp as claimed in claim 2 in which said pressure foot is provided with a guide rod, a pin pivotally mounted on said housing and having an aperture therein to receive said rod in sliding relation thereto,

and in which one' end of said spring bears against said pivot and the other end of said spring bears against said pressure foot.

4. A lifting clamp as claimed in claim 2 including a lever link pivotally mounted on said housing on an axis concentric with the axis of said radius link, said lever link being pivotally connected to said pressure foot.

5. A lifting clamp comprising a housing having fixed and movable jaws between which a load may be clamped, a radius link pivotally mounted on said housing, said radius link having arms extending in opposite directions from the pivot, means for connecting one arm of said radius link to said movable jaw to move said jaw between open and closed positions, a toggle joint comprising a lever link pivotally mounted on said housing on an axis concentric with the axis of said radius link and constituting one leg of the toggle joint and a pressure foot pivotally connected to said lever link and constituting the other leg of the toggle joint, and means to apply spring pressure to said toggle joint to cause said pressure foot to engage and apply pressure to one arm of said radius link in one position of said toggle joint and to cause said pressure foot to engage and apply pressure to the other arm of said radius link in another position of said toggle joint.

6. A lifting clamp as claimed in claim 5 including a hand lever pivotally mounted on said housing on an axis concentric with said radius link and said lever link and operatively connected to said lever link to move said toggle joint from one position to another.

7. A lifting clamp as claimed in claim 5 in which said pressure foot is provided with a guide rod pivotally connected to said housing, said rod being in sliding engagement with the pivot, and in which one end of said spring bears against said pivot and the other end of said spring bears against said pressure foot.

8. A lifting clamp as claimed in claim 7 in which said pivotal connection between said lever link and said pressure foot lies on one side of a line connecting the axis of said lever link pivot with the axis of said rod pivot in one position of said toggle, and passes over center to lie on the other side of said line in another poness of the load which is gripped. 

1. A lifting clamp comprising a housing having fixed and movable jaws between which a load may be clamped, a radius link pivotally mounted on said housing, said radius link having arms extending in opposite directions from the pivot, means including a link pivotally connecting one arm of said radius link to said movable jaw to move said jaw between open and closed positions, a spring, and means to transmit pressure from said spring to one arm of said radius link when said link is in jaw opening position and to transmit pressure from said spring to the other arm of said link when said link is in jaw closing position.
 2. A lifting clamp as claimed in claim 1 in which said pressure transmitting means includes a pressure foot having a heel positioned to engage a surface of one arm of said radius link when said link is in jaw opening position and having a toe positioned to engage a surface of the other arm of said radius link when said link is in jaw closing position.
 3. A lifting clamp as claimed in claim 2 in which said pressure foot is provided with a guide rod, a pin pivotally mounted on said housing and having an aperture therein to receive said rod in sliding relation thereto, and in which one end of said spring bears against said pivot and the other end of said spring bears against said pressure foot.
 4. A lifting clamp as claimed in claim 2 including a lever link pivotally mounted on said housing on an axis concentric with the axis of said radius link, said lever link being pivotally connected to said pressure foot.
 5. A lifting clamp comprising a housing having fixed and movable jaws between which a load may be Clamped, a radius link pivotally mounted on said housing, said radius link having arms extending in opposite directions from the pivot, means for connecting one arm of said radius link to said movable jaw to move said jaw between open and closed positions, a toggle joint comprising a lever link pivotally mounted on said housing on an axis concentric with the axis of said radius link and constituting one leg of the toggle joint and a pressure foot pivotally connected to said lever link and constituting the other leg of the toggle joint, and means to apply spring pressure to said toggle joint to cause said pressure foot to engage and apply pressure to one arm of said radius link in one position of said toggle joint and to cause said pressure foot to engage and apply pressure to the other arm of said radius link in another position of said toggle joint.
 6. A lifting clamp as claimed in claim 5 including a hand lever pivotally mounted on said housing on an axis concentric with said radius link and said lever link and operatively connected to said lever link to move said toggle joint from one position to another.
 7. A lifting clamp as claimed in claim 5 in which said pressure foot is provided with a guide rod pivotally connected to said housing, said rod being in sliding engagement with the pivot, and in which one end of said spring bears against said pivot and the other end of said spring bears against said pressure foot.
 8. A lifting clamp as claimed in claim 7 in which said pivotal connection between said lever link and said pressure foot lies on one side of a line connecting the axis of said lever link pivot with the axis of said rod pivot in one position of said toggle, and passes over center to lie on the other side of said line in another position of said toggle.
 9. A lifting clamp as claimed in claim 5 in which said radius link is provided with a concavely curved surface and said pressure foot is provided with a convexly curved surface positioned to engage said concavely curved surface when said toggle joint is moved to cause said pressure foot to engage said radius link.
 10. A lifting clamp as claimed in claim 9 in which the point of engagement between said convexly and concavedly curved surfaces varies depending on the thickness of the load which is gripped. 